T cell receptor (TCR) provides the specificity of antigen-recognition for T cells. A competent T cell immune system depends on a diverse TCR repertoire. However, information on human and mouse TCR repertoires in general and to defined viral antigens is relatively limited. We performed a comprehensive analysis of TCR repertoires of human CD8+ TCR repertoires specific for two dominant viral epitopes: pp65 (NLV) of cytomegalovirus and M1 (GIL) of influenza A virus using the high-throughput sequencing (HTS) and single-cell paired TCR analysis and mouse CD4 T cell subsets including nave, memory, and regulatory T cells. Our analysis of antigen-specific CD8+ TCR repertoires resulted in identification of thousands of new NLV- and GIL-specific alpha and beta TCR sequences and dozens of distinct CDR3 and CDR3 consensus motifs. This diversity is substantially greater than previously described for T cell responses to single viral epitopes, both for private and public TCR clonotypes, and exhibited a high degree of individual variations (875,533 TCR-alpha or beta per subject). However, diversity is effectively restricted by preferential V-J combinations, CDR3 lengths, and CDR3/CDR3 pairings. Structures of two GIL-specific TCRs bound to GILHLA-A2 provided a potential explanation for the lower diversity of GIL-specific than NLV-specific repertoires. These anti-viral TCRs occupied up to 3.4% of the CD8+ TCR repertoire, ensuring broad T cell responses to single epitopes. Our comprehensive genetic, biochemical, and structural portrait of two different anti-viral T cell responses may contribute to the future development of predictors of immunity or disease at the personal level. Mouse is the most studied model of immune system and yet the information of alpha/beta TCR repertoire is limited. Here we applied high throughput sequencing with unique molecular identifier to determine TCR-alpha and TCR-beta sequences from approximately 14% of total CD4+ T cells in a C57BL/6 mouse. We have identified 1.67 x 105 unique TCR-alpha and 2.34 x 105 unique TCR-beta sequences with projected TCR-alpha and TCR-beta repertoires 2.79 x 106 and 5.09 x 106, respectively. The repertoire of TCR-beta was 1.6-1.8 time larger than that of TCR-alpha, and nave TCR-alpha and TCR-beta repertoires were 2.0 and 1.7 larger than those of memory CD4+ T cells, respectively. Nave and memory CD4+ T cells had substantial overlapping TCR sequences, reflecting relative small size of the repertoires. CD5hi memory CD4+ T cells have higher affinity than CD5lo memory CD4+ T cells but their Alpha/beta TCR repertoires were not significantly different. Alpha/beta TCR repertoires of regulatory (Treg) CD4+ T cells was between nave and memory T cells and a fraction of Treg (15%) consists of distinct CDR3 amino acid sequences of TCR-alpha (5.2 x 103) and TCR-beta (9.7 x 103), may represent the natural Treg derived from thymus. Together, these findings provide the depth information of alpha/betaTCR repertoire of mouse CD4+ T cells for the first time and serve as a foundation for further elucidating the broadness and specificity of CD4+ T cell repertoire.